The present invention relates, in general, to subsea well apparatus and is directed specifically to subsea well apparatus such that, in only one trip between the vessel or platform on the water surface and the subsea well, a casing string is run into the well bore and cemented in place, a wear bushing is positioned within the well bore for protecting the surrounding wellhead during subsequent drilling operations, and the annular seal region between a casing hanger body and the surrounding wellhead bore is sealed and tested.
More specifically, in the drilling of oil and gas wells at an underwater location, a casing string is run into a well bore, and supported by a casing hanger (also referred to as hanger body) resting on complementary seats within a surrounding wellhead. After the casing string is cemented in place, a suitable seal assembly, referred to as a packoff assembly, is actuated (energized) to packoff (seal) the annular seal region (gland) between the exterior of the casing hanger and the surrounding wellhead for later drilling operations to take place within the wellhead. Energizing the packoff (seal) is also referred to as setting the packoff. Apparatus for such operations is illustrated in a number of U.S. patents, such as, for example, U.S. Pat. Nos. 3,313,030, 3,468,558, 3,468,559, 3,489,436, 3,492,026, 3,797,864 and 3,871,449. These patents show examples of casing hangers (hanger bodies), packoff assemblies with deformable elastomeric packing seals (packoffs), and seat protectors (now called wear bushings depending on their function, although in these patents, the terms were used interchangeably), being lowered into position in one trip of the running tool between the vessel or platform and the well.
Reference is also made to the U.S. patent application of Goris and Pettit, Ser. No. 719,383, filed Apr. 2, 1985 entitled "Casing Hanger and Running Apparatus", which disclosed apparatus in which seating the casing hanger within the wellhead, cementing the casing hanger in place, packing off the seal region and pressure testing off the seal for leakage is accomplished in one trip between the vessel or platform and the well. However, no wear bushing is disclosed in this referenced application.
Another U.S. patent application of John Pettit entitled "Casing Hanger Running Tool", Ser. No. 727,491, filed Apr. 26, 1985 discloses a running tool which, among other things, will position a casing hanger and a wear bushing in one trip with the wear bushing positioned in its final position upon the landing of the running tool in the wellhead.
This invention improves such apparatus by having a running tool engage one piece of a two piece wear bushing instead of engaging the casing hanger as in the prior art apparatus. The engaged piece supports a packoff drive nut of a packoff assembly which, in turn, supports a casing hanger. The other piece of the wear bushing is used to drive the packoff assembly to seal an annular seal region between the casing hanger and surrounding well bore. With this arrangement, one running tool is usable with varying sizes of casing hangers.
This invention also includes means by which the running tool can be released rapidly prior to moving the seal into the annular seal region and means by which an engaged piece of the wear bushing is positioned in its final operating position when the apparatus is initially landed in the well bore. Also included in the means for rapid release of the running tool is means for releasing the drive elements of the running tool upon application of low torque and a safety feature to prevent accidental release of the running tool.